diff --git a/small_small_hr/forms.py b/small_small_hr/forms.py
index a8d7343..778c49a 100644
--- a/small_small_hr/forms.py
+++ b/small_small_hr/forms.py
@@ -4,6 +4,7 @@
 from datetime import datetime, time
 
 from django import forms
+from django.db.models import Q
 from django.conf import settings
 from django.contrib.auth.models import User
 from django.utils.translation import ugettext as _
@@ -102,11 +103,29 @@ def clean(self):
         cleaned_data = super().clean()
         end = cleaned_data.get('end')
         start = cleaned_data.get('start')
+        date = cleaned_data.get('date')
+        staff = cleaned_data.get('staff')
 
         # end must be later than start
         if end <= start:
             self.add_error('end', _("end must be greater than start"))
 
+        # must not overlap within the same date
+        # pylint: disable=no-member
+        overlap_qs = OverTime.objects.filter(
+            date=date, staff=staff, status=OverTime.APPROVED).filter(
+                Q(start__gte=start) | Q(end__lte=end))
+
+        if self.instance is not None:
+            overlap_qs = overlap_qs.exclude(id=self.instance.id)
+
+        if overlap_qs.exists():
+            msg = _('you cannot have overlapping overtime hours on the '
+                    'same day')
+            self.add_error('start', msg)
+            self.add_error('end', msg)
+            self.add_error('date', msg)
+
 
 class ApplyOverTimeForm(OverTimeForm):
     """
@@ -253,6 +272,20 @@ def clean(self):
                 self.add_error('start', msg)
                 self.add_error('end', msg)
 
+        # must not overlap
+        # pylint: disable=no-member
+        overlap_qs = Leave.objects.filter(
+            staff=staff, status=Leave.APPROVED, leave_type=leave_type).filter(
+                Q(start__gte=start) | Q(end__lte=end))
+
+        if self.instance is not None:
+            overlap_qs = overlap_qs.exclude(id=self.instance.id)
+
+        if overlap_qs.exists():
+            msg = _('you cannot have overlapping leave days')
+            self.add_error('start', msg)
+            self.add_error('end', msg)
+
 
 class ApplyLeaveForm(LeaveForm):
     """
diff --git a/tests/test_forms.py b/tests/test_forms.py
index 117e85b..d815ad8 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -91,6 +91,51 @@ def test_overtime_form_apply(self):
         self.assertEqual(OverTime.PENDING, overtime.status)
         self.assertEqual('', overtime.comments)
 
+    def test_overtime_form_apply_no_overlap(self):
+        """
+        Test no overlaps on OverTime
+        """
+        user = mommy.make('auth.User', first_name='Bob', last_name='Ndoe')
+        staffprofile = mommy.make('small_small_hr.StaffProfile', user=user)
+
+        request = self.factory.get('/')
+        request.session = {}
+        request.user = AnonymousUser()
+
+        # 6 hours of overtime
+        start = datetime(
+            2017, 6, 5, 0, 0, 0, tzinfo=pytz.timezone(settings.TIME_ZONE))
+        end = datetime(
+            2017, 6, 5, 6, 0, 0, tzinfo=pytz.timezone(settings.TIME_ZONE))
+
+        mommy.make(
+            'small_small_hr.OverTime', start=start.time(), end=end.time(),
+            status=OverTime.APPROVED, date=start.date, staff=staffprofile)
+
+        data = {
+            'staff': staffprofile.id,
+            'date': start.date(),
+            'start': start.time(),
+            'end': end.time(),
+            'reason': 'Extra work',
+        }
+
+        form = ApplyOverTimeForm(data=data)
+        self.assertFalse(form.is_valid())
+        self.assertEqual(3, len(form.errors.keys()))
+        self.assertEqual(
+            'you cannot have overlapping overtime hours on the same day',
+            form.errors['start'][0]
+        )
+        self.assertEqual(
+            'you cannot have overlapping overtime hours on the same day',
+            form.errors['date'][0]
+        )
+        self.assertEqual(
+            'you cannot have overlapping overtime hours on the same day',
+            form.errors['end'][0]
+        )
+
     def test_overtime_form_process(self):
         """
         Test OverTimeForm
@@ -208,6 +253,53 @@ def test_leaveform_apply(self):
         self.assertEqual(Leave.PENDING, leave.status)
         self.assertEqual('', leave.comments)
 
+    def test_leaveform_no_overlap(self):
+        """
+        Test LeaveForm no overlap
+        """
+        user = mommy.make('auth.User', first_name='Bob', last_name='Ndoe')
+        staffprofile = mommy.make('small_small_hr.StaffProfile', user=user)
+        staffprofile.leave_days = 21
+        staffprofile.sick_days = 10
+        staffprofile.save()
+
+        request = self.factory.get('/')
+        request.session = {}
+        request.user = AnonymousUser()
+
+        # 6 days of leave
+        start = datetime(
+            2017, 6, 5, 0, 0, 0, tzinfo=pytz.timezone(settings.TIME_ZONE))
+        end = datetime(
+            2017, 6, 10, 0, 0, 0, tzinfo=pytz.timezone(settings.TIME_ZONE))
+
+        mommy.make('small_small_hr.AnnualLeave', staff=staffprofile, year=2017,
+                   leave_type=Leave.REGULAR, carried_over_days=12)
+
+        mommy.make('small_small_hr.Leave', leave_type=Leave.REGULAR,
+                   start=start, end=end, status=Leave.APPROVED,
+                   staff=staffprofile)
+
+        data = {
+            'staff': staffprofile.id,
+            'leave_type': Leave.REGULAR,
+            'start': start,
+            'end': end,
+            'reason': 'Need a break',
+        }
+
+        form = ApplyLeaveForm(data=data)
+        self.assertFalse(form.is_valid())
+        self.assertEqual(2, len(form.errors.keys()))
+        self.assertEqual(
+            'you cannot have overlapping leave days',
+            form.errors['start'][0]
+        )
+        self.assertEqual(
+            'you cannot have overlapping leave days',
+            form.errors['end'][0]
+        )
+
     def test_leaveform_admin(self):
         """
         Test LeaveForm apply for leave